Substantial variation in leaf senescence times

Posted by Amanda Gallinat, photos by Richard Primack

"October is the month of painted leaves.  Their rich glow now flashes round the world." 

-Henry David Thoreau, "Autumnal tints” in Excursions

In recent years, the Primack lab has worked in partnership with 5 other research groups at botanic gardens around the world to monitor the timing of leaf senescence (leaf color change and leaf drop) across a wide range of species. The results of this international collaboration have been published in Annals of Botany, in a paper led by Zoe Panchen of Carleton University.

Prunus sargentii leaves changing from green to yellow and red coloration.

The paper, entitled "Substantial variation in leaf senescence times among 1360 temperate woody plant species: implications for phenology and ecosystem processes" demonstrates that autumn leaf senescence dates vary broadly between species and botanic gardens. Within each botanic garden, the sequence of leaf senescence was fairly consistent between years, but did not have a strong phylogenetic signal. 

Leaves senescing in the Morus section of the Arnold Arboretum in Boston, MA

These results are in stark contrast with the results of a similar study on spring leaf-out times that our botanic garden collaborative published last year, which showed that the sequence of leaf-out is largely consistent between years and locations, and contains strong phylogenetic patterns. We conclude that while leaf-out is strongly driven by spring temperatures, the lack of patterns in leaf senescence timing means it is likely driven by a combination of local environmental factors, including soil moisture, frost, wind, and temperature.

Hossein Akhani from Iran visits Primack Lab

Posted by Richard Primack

In early July, Prof. Hossein Akhani from the University of Tehran visited the Primack lab to discuss our current project to produce an Iranian edition of A Primer of Conservation Biology. Prof. Akhani presented an engaging seminar to the BU Biology Department on “The ecology and conservation of saline ecosystems in Iran with a focus on Lake Urmia, the largest lake in the Middle East”. The environmental damage being done to Lake Urmia through diversion of water is reminiscent of the better known example of the disappearance of the Aral Sea.  

Two highlights of his visit were a trip to the Arnold Arboretum with BU undergrads Luca Russo and Lucas Stegman to monitor fruit maturation, and an excursion to Plum Island to observe coastal vegetation.  

Prof. Akhani’s visit coincided with the final round of international negotiations regarding Iran’s nuclear program, and allowed us to get a better idea of the Iranian perspective of these complex issues.

The Primack Lab visits Manomet for spring migration

Posted by Amanda Gallinat

Last month, the Primack Lab visited Manomet Center for Conservation Sciences in Plymouth, MA to see the landbird banding program in action. This year is Manomet's 48th year of banding, and their long-term records of landbird passage dates have allowed us to explore how the timing of bird migration is changing over time and in response to climate change, in both spring and autumn. 

This American Redstart was captured during our visit to Manomet's banding lab

Our group included Richard Primack, myself, and two undergraduate assistants in the lab, Luca Russo and Lucas Stegman. Luca and Lucas have both assisted with sorting and identifying seeds from songbird fecal samples collected at Manomet last autumn. During our visit, they got a chance to see the banding process first-hand, walk the net lanes at Manomet, and observe many of the species that provided the fecal samples we've been sorting.

Lucas observes a House Wren before it is released by the banders

Luca and bander Mattie Vandenboom with a Gray Catbird that has just been processed

We are grateful to banding director Trevor Lloyd-Evans and the spring 2015 banders for their wonderful hospitality, and we look forward to returning for more banding in the fall! 

Of Looms and Lilies: An experimental dance performance inspired by Thoreau’s phenology observations

Posted by Richard B. Primack

Recently, dancers from Weber Dance in Somerville, MA, have put on a new production, entitled Of Looms and Lilies. This work is inspired in part by the research of our group, as described on their website: “In 1845 Henry David Thoreau retreated to his cabin at Walden Pond in Massachusetts to experiment with a life of simplicity. He kept detailed records of his environment including when the pond froze and thawed and when each variety of plant bloomed in spring.” Weber Dance recognizes our work that “those same plants are blooming an average of three weeks earlier than they did in 1845. It is no longer disputed that human activity is contributing to climate change, so what have we gained and what are we losing?”

Weber Dance uses this material to develop “an artistic investigation of the proliferation of material wealth generated by the industrial revolution and its effect on both our personal and spiritual lives and its wider impact on climate change. It is also a simple conversation between a nineteenth century factory worker and a contemporary woman. What might they say to one another? What might they learn?”

For more information, see http://www.weberdance.com/index.html

Remote Sensing at Acadia National Park, Part 2

Yan Liu from School for the Environment, University of Massachusetts Boston joined Caitlin for the week of June 8^th to walk the phenology transects up and down three mountains at Acadia National Park on Mount Desert Island in Maine. Her goal was to make comparison of leaf out phenology data from these three transects with 30m resolution imagery of leaf out times from two Landsat satellites,  Landsat 7 and Landsat 8. The two satellites normally overfly an area on the Earth once every 8 days, but we are fortunately that the Acadia region lies in the overlap area between swaths and therefore is imaged on two subsequent days during an 8 day period. This maximizes our opportunities to get a cloud free image of the area and adequately capture the phenology of leaf out from space. We are interested in seeing how well the relatively coarse resolution Landsat imagery can capture the elevational differences of leaf out that Caitlin is recording on the ground.

These two Landsat 8 true color composite images show the changes that have been occurring during the spring green up of the vegetation at Acadia in 2014.  On May 7 the deciduous trees and shrubs on the mountains of Mount Desert Island are still mostly leafless, while by June 8 they have leafed out.

Humboldt was an inspiration for Thoreau

Posted by Richard Primack

Last week I traveled to Berlin for the annual meeting of the Humboldt Foundation of the government of Germany where I was recognized for receiving a Humboldt Research Award. This award is “granted in recognition of a researcher's entire achievements to date to academics whose fundamental discoveries, new theories, or insights have had a significant impact on their own discipline and who are expected to continue producing cutting-edge achievements in the future.” I received this Humboldt award for research on using the records of Thoreau to detect the impacts of climate change. This seems particularly appropriate because Alexander von Humboldt’s ability to carefully observe and detect rational explanations and patterns in nature was an inspiration for Thoreau.

I also visited the Berlin Botanical Garden to meet with Birgit Nordt and Albert-Dieter Stevens who are part of our international network of botanical gardens monitoring leafing out, leaf senescence and fruiting times. I was amazed by enormous variety of plants being grown in the outdoor alpine gardens and in the extensive greenhouses.

I presented a seminar at the University of Potsdam. The Ecology program is located on the grounds of Sanssucci garden, which includes many palaces built by the Prussian kings.  One of the palaces had extensive south-facing terraces on which grape vines and fig trees were grown in vertical cold frames. 

And finally, I met researchers at the Berlin Museum, and toured both the research collections and public displays. Their dinosaur display is claimed to have the greatest vertical height of any dinosaur display in the world.

Yanjun Du visits the Primack Lab

Posted by Amanda Gallinat

Recently, the Primack Lab received a visit from our colleague Yanjun Du.

Du is an assistant professor at the Chinese Academy of Sciences, and has collaborated with the Primack Lab on several international projects, including a recently published study of autumn leaf phenology at six botanical gardens. Du shares many of our lab’s interests, including the effects of climate change on phenology and using herbarium specimens to investigate long-term phenology patterns.

Du is currently a visiting researcher at Yale University, so he joined us in Boston for a day of exchanging ideas and discussing current and future projects. I was particularly delighted to show Du one of our ongoing projects, in action, for which we are identifying the seeds from songbird fecal samples to identify what they are eating during autumn migration.

We look forward to our next visit and future collaborations with Du!